A filter is a device which allows useful signals to pass while inhibiting interference signals. At present, base station filters available in the market mainly are metallic cavity filters. With the development of communication technologies and the intensive utilization of frequency spectrum resources, a radio system has higher requirements in the radio signals, and demands high-power transmitting and high-sensitivity receiving. However, the performance and volume of metallic cavity filters cannot satisfy these requirements; under such a circumstance, a dielectric filter is becoming widely used due to its low loss.
The dielectric constant of a Transverse Magnetic (TM) dielectric filter is the key factor to determine the size of the filter. At present, mature products available in the market are two types of dielectric resonators, where one type of dielectric resonator has a dielectric constant being 35 and the other type of dielectric resonator has a dielectric constant being 45. The two types of dielectric resonators have a relatively larger size in the low communication frequency band and require a larger single-cavity volume. For example, a dielectric resonator and a dielectric filter are provided in the related art. As shown in FIG. 1, the dielectric resonator includes a dielectric resonant column 102 and a metallic cavity 104, wherein the dielectric resonant column 102 is located in the metallic cavity 104, and the bottom of the dielectric resonant column 102 contacts the bottom of the metallic cavity 104; the dielectric resonator further includes a cover plate 103 and a conducting elastomer 101, wherein the cover plate 103 is used to seal the metallic cavity 104; the conducting elastomer 101 is located between the cover plate 103 and the dielectric resonant column 102 to connect the cover plate 103 and the dielectric resonant column 102. The dielectric filter ensures a fine contact between the dielectric resonant column and the cover plate relying on the resilience of the conducting elastomer caused by compression. The dielectric resonator is connected only by several contacts of a reed; moreover, when the cavity is expanded or contracted with the temperature, the contact area and the contact depth of the contact also changes, thereby leading to a change in the performance characteristic of the filter. The dielectric resonator has a relatively lower efficiency and a relatively larger volume.
In view of the problem that the dielectric filter in the related art has a low space utilization rate and has a large volume in a low frequency band, no solution has been proposed so far.